Ultrathin copper foil with carrier and printed circuit board using same

ABSTRACT

An ultrathin copper foil with a carrier not causing blistering at a release layer interface, having a low carrier peeling force, friendly to the environment, and enabling easy peeling of a carrier foil and an ultrathin copper foil even under a high temperature environment and a printed circuit board enabling a stable production quality of a base of a printed circuit board for fine pattern applications using the ultrathin copper foil with the carrier, that is, an ultrathin copper foil with a carrier comprising a carrier foil, a release layer, and an ultrathin copper foil, wherein the release layer is formed by a metal A for retaining a release property and a metal B for facilitating plating of the ultrathin copper foil, a content a of the metal A and a content b of the metal B forming the release layer satisfying an equation:
 
10≦ a /( a+b )*100≦70
 
and a printed circuit board prepared by using such an ultrathin copper foil with a carrier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and the benefit of Japanese PatentApplication No. 2005-361311 filed Dec. 15, 2005 and Japanese PatentApplication No. 2006-303302 filed Nov. 8, 2006, the entire contents ofwhich are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an ultrathin copper foil with a carrierand a printed circuit board using the ultrathin copper foil with thecarrier, more particularly relates to an ultrathin copper foil with acarrier suitable for a printed circuit board for high density ultrafinecircuit (fine pattern) applications, a multi-layer printed circuitboard, and a chip-on-film use circuit board.

2. Description of the Related Art

Usually, in the copper foil used for a printed circuit board forming thebase of a printed circuit board, a multi-layer printed circuit board, achip-on-film use circuit board, or the like, a surface on the side heatpressed to a plastic substrate or the like is formed as a roughenedsurface and this roughened surface is used to manifest an anchor effectwith respect to the substrate so as to raise a bond strength between thesubstrate and the copper foil and thereby to secure reliability as aprinted circuit board.

Further, recently, copper foil with a resin layer formed by covering theroughened surface of copper foil by a bonding use resin such as an epoxyresin in advance and using the bonding use resin as an insulating resinlayer of a semi-cured state (B stage) is used as copper foil for forminginterconnects. The side with the insulating resin layer is hot pressedto a substrate to form a printed circuit board. Such printed circuitboards are stacked in multiple layers to thereby produce a builtupcircuit board. A builtup circuit board is one type of multi-layerprinted circuit board and is obtained by forming an insulating layer anda conductive pattern on the insulating substrate one layer at a time inthat order, plating holes (vias) formed by a laser process or a photoprocess, and stacking such circuit layers while connecting the layers.

In this circuit board, the vias can be made finer corresponding to thehigher integration of various types of electronic devices. Therefore,interconnect patterns are increasingly being required to be made finerin line widths and line pitches. For example, in the case of printedcircuit boards used in semiconductor packages, provision of printedcircuit boards having high density ultrafine interconnects having linewidths and line pitches of approximately 30 μm is being demanded.

When using thick copper foil as the copper foil for such a fine patternprinted circuit board, an etching time at the time of formation of theinterconnects and circuits by etching becomes long. As a result, averticalness of side walls of the formed interconnect patterns is lost.When the interconnect line widths of the formed interconnect patternsare narrow, this sometimes leads to disconnection. Accordingly, as thecopper foil used for fine pattern applications, copper foil having athickness of 9 μm or less is required. At present, copper foil having athickness of about 5 μm is most frequently used. Further thinner copperfoil is being sought.

However, such thin copper foil (hereinafter sometimes also referred toas “ultrathin copper foil”) has a weak mechanical strength, is easilywrinkled or creased at the time of the production of the printed circuitboard, and sometimes even breaks. Therefore, as the ultrathin copperfoil used for the fine pattern applications, use is made of an ultrathincopper foil with a carrier formed by directly electrodepositing anultrathin copper foil layer on one surface of metal foil serving as acarrier (hereinafter, referred to as “carrier foil”) via a releaselayer.

As explained above, the copper foil having a thickness of 5 μm which isfrequently used at present is provided as the ultrathin copper foil withthe carrier.

The ultrathin copper foil with the carrier has a carrier foil on onesurface of which a release layer and ultrathin copper foil deposited byelectric copper plating are formed in that order. The outermost layersurface of the ultrathin copper foil made of the electric copper platingis finished to a roughened surface.

As the release layer formed on the one surface of the carrier foil, anorganic coating film, Cr metal, Cr alloy, chromate, etc. are usuallyused, but in recent years in interconnect substrates using a polyamideor other high temperature plastic etc. as the insulating substrate, theconditions such as the pressing temperature of the copper foil and thesubstrate or the curing temperature are high temperature, therefore anorganic release layer can no longer be peeled off. Therefore, an organiccoating film cannot be used, and a metal-based release layer is usedinstead.

As the metal for forming the release layer, as described before, a Crmetal, Cr alloy, and chromate form the mainstream. However, when usingCr for the release layer, blistering occurs in the high temperatureprocess of production of the interconnect substrates, variation occursin the release properties, and some problem arises in stability ofproduction of the interconnect substrates.

Further, some metals such as Cr reportedly exert an adverse influenceupon the human body. A future ban on use of these metals may even beexpected. Accordingly, in actual circumstances, the use of a metal suchas Cr must be prevented as much as possible.

Summarizing the problems in the art, as explained above, a release layerusing Cr results in insufficient stability of high temperatureproduction of the interconnect substrates. The appearance of theultrathin copper foil with the carrier using a release layer not usingCr metal liable to have an effect on the human body or suppressing thecontent of Cr to the smallest limit and enabling easy release even undera high temperature has therefore been desired.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an ultrathin copperfoil with a carrier suppressing the occurrence of blistering, notexerting an influence upon carrier peeling, having a wide range ofpossible production conditions, stable in production quality, friendlyto the environment, and enabling easy peeling of the carrier foil andthe ultrathin copper foil even when placed in a high temperatureenvironment.

Another object of the present invention is to provide a printed circuitboard forming the base of a printed circuit board for fine patternapplications using the ultrathin copper foil with the carrier, amulti-layer printed circuit board, a chip-on-film use circuit board, orthe like.

A first ultrathin copper foil with a carrier of the present invention isan ultrathin copper foil with a carrier comprising a carrier foil, arelease layer, and an ultrathin copper foil, wherein the release layerincludes a metal A for retaining a release property and a metal B forfacilitating plating of the ultrathin copper foil, and a content a ofthe metal A and a content b of the metal B constituting the releaselayer satisfy an equation:10≦a/(a+b)*100≦70(%)

A second ultrathin copper foil with a carrier of the present inventionis an ultrathin copper foil with a carrier comprising a carrier foil,release layers, and an ultrathin copper foil, wherein the release layersare comprised of two layers having different composition ratios of ametal A for retaining a release property and a metal B for facilitatingplating of the ultrathin copper foil, and, when the content of the metalA constituting a release layer on the carrier foil side is c, thecontent of the metal B thereof is d, the content of the metal Aconstituting a release layer on the ultrathin copper foil side is e, andthe content of the metal B thereof is f, an equation of:|c/(c+d)−e/(e+f)|*100≧3(%)is satisfied.

Preferably, the metal A constituting the release layers is selected froma group consisting of Mo, Ta, V, Mn, W, and Cr, and the metal B isselected from a group consisting of Fe, Co, Ni, and Cr.

Preferably, a total of the amount(s) of deposition of the releaselayer(s) is 0.05 mg/dm² to 50 mg/dm².

The printed circuit board of the present invention is a printed circuitboard for high density ultrafine interconnect applications comprisingthe ultrathin copper foil with the carrier with the ultrathin copperfoil laminated on a resin substrate.

According to the present invention, therefore, an ultrathin copper foilwith a carrier suppressing the occurrence of blistering, not exerting aninfluence upon carrier peeling, having a wide range of possibleproduction conditions, stable in production quality, friendly to theenvironment, and enabling easy peeling of the carrier foil and theultrathin copper foil even when placed in a high temperature environmentcan be provided.

Further, according to the present invention, a printed circuit boardforming the base of a printed circuit board for fine patternapplications using the ultrathin copper foil with the carrier, amulti-layer printed circuit board, a chip-on-film use circuit board, orthe like can be provided.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

As the metal carrier foil for an ultrathin copper foil with a carrier,generally use can be made of aluminum foil, aluminum alloy foil;stainless steel foil, titanium foil, titanium alloy foil, copper foil,copper alloy foil, and so on. From the viewpoint of the convenience ofhandling of the carrier foil used as the ultrathin copper foil or copperalloy foil (hereinafter referred to all together as “ultrathin copperfoil” when not necessary to differentiate these), preferably use is madeof electrolytic copper foil, electrolytic copper alloy foil, rolledcopper foil, or rolled copper alloy foil. Further, as the thicknessthereof, preferably use is made of foil having a thickness of 7 μm to200 μm.

When employing thin copper foil having a thickness of less than 7 μm asthe carrier foil, since this carrier foil is weak in mechanicalstrength, it easily wrinkles and creases and is liable to tear at thetime of production of printed circuit boards etc. Further, when thethickness of the carrier foil becomes more than 200 μm, an increase ofweight per unit coil (coil unit weight) exerts a big influence upon theproductivity. At the same time, a larger strength is required facilitywise as well. The facility ends up becoming large in size, so this isnot preferred. Accordingly, as the thickness of the carrier foil, 7 μmto 200 μm is preferred.

As the carrier foil, preferably use is made of a metal foil having asurface roughness Rz of at least one side of 0.01 μm to 5.0 μm.Particularly, in a case where visual recognizability on a chip-on-filmuse circuit board is required, preferably the Rz is 0.01 μm to 2.0 μm.For this reason, when visual recognizability on a chip-on-film usecircuit board is required, when using a carrier foil having a range ofsurface roughness Rz of 2 μm to 5.0 μm, mechanical polishing orelectrolytic polishing may be applied to the rough surface in advance tosmooth the surface for use so that the surface roughness Rz becomes 0.01μm to 2 μm in range. Note that it is also possible to previously applymechanical polishing and/or electrochemical dissolution to carrier foilhaving a surface roughness Rz of 5 μm or more so as to smooth it foruse.

In the present invention, the release layer provided on the carrier foilis constituted by a metal and a nonmetallic or metallic oxide or alloymixed together. Particularly, the release layer of the present inventionis constituted by a metal A for retaining the release property and ametal B facilitating the plating of the ultrathin copper foil.

In the present invention, the metal A constituting the release layer isselected from a group consisting of Mo, Ta, V, Mn, W, and Cr.

Further, the metal B is selected from a group consisting of Fe, Co, Ni,and Cr.

Note that Cr metal has environmental problems, therefore particularlypreferably as much as possible it is not used at all or, even if used,the amount of use is suppressed to the required lowest limit.

In the present invention, when there is a single release layer, itincludes any of the group of metals A acting to retain the releaseproperty and any of the group of metals B facilitating the plating ofthe ultrathin copper foil. The ratio of the meal A and the metal Bpreferably satisfies the equation:10≦a/(a+b)*100≦70wherein the amount of metal deposition of the group of the metals A perunit area of 1 dm² is a (mg) and the amount of metal deposition of thegroup of the metals B is b (mg).

If the ratio of the metal A and the metal B is less than 10%, thecarrier peeling force becomes stronger and the ultrathin copper foil isliable not to be able to be peeled off. Further, if becoming a valuelarger than 75%, the possibility arises that a sound plating cannot beformed on the release layer. The ratio is particularly preferably 25% to65%. Note that when two or more types of metals of the same group areincluded, the total of these metals is used as the amount of deposition.

Note that the release layer of the above composition ratio need only bethe above composition ratio at the portion of the thickness of 0.0001 μmto 0.01 μm from the surface of the carrier foil.

In the ultrathin copper foil with the carrier of the present invention,it is possible to provide two release layers so as to further stabilizethe peeling property and suppressing blistering. When providing tworelease layers, the composition ratios of the metal A for retaining therelease property and the metal B for facilitating the plating of theultrathin copper foil preferably satisfies the equation:|c/(c+d)−e/(e+f)|*100≧3(%)where the content of the metal A constituting the release layer on thecarrier foil side is c, the content of the metal B thereof is d, thecontent of the metal A constituting the release layer on the ultrathincopper foil side is e, and the content of the metal B thereof is f.

Note that the effects are further improved when the layers satisfy theequations of:10≦c/(c+d)*100≦70 and10≦e/(e+f)*100≦70

The above two layers, or layers more than that, may be formed by platingsolutions deliberately changed in compositions or may be formed by achange of the composition ratios between the carrier foil surface sideand the ultrathin copper foil side due to the plating conditions ratherwithout a change of the compositions of the plating solutions. If adifference of upper and lower composition ratios is 3% or more in thethicknesses of 0.1% to 5% of the overall deposition amounts from thecarrier foil side and the ultrathin copper foil side, effects equivalentto those by deliberately changing the compositions of two layers arecreated.

When providing two release layers constituted by different types ofmetals, equivalent effects can be created if the metal species belongingto the metal A and the metal species belonging to the metal B are in theabove ranges of composition ratios.

In the present invention, the total of the deposition amounts of thedeposited release layers is preferably 0.05 mg/dm² to 50 mg/dm². If lessthan 0.05 mg/dm², the layers do not sufficiently function as releaselayers, while even when the total of the deposition amounts exceeds 50mg/dm², while the layers can be peeled off, the metal species formingthe release layers is a hard-to-plate metal, therefore if the layers areformed thick, the smoothness is lost, variation is seen in peelingforce, the stability is lost, and blistering is even caused, sopreferably the total is 50 mg/dm² or less. Further, when consideringalso the smoothness of the surface of the ultrathin copper foil, thetotal is preferably 20 mg/dm² or less. Further, preferably the roughnessof the release layer surface is 1.5 times or less the roughness of thecarrier foil surface, and also the surface area is 1.5 times or less thesurface area of the carrier foil. This is because when the surfaceroughness and the surface area become large, these overall make thecarrier peeling force large and also make the variation large.

In the present invention, the thickness in the case where there are tworelease layers is 0.05 mg/dm² to 50 mg/dm² in terms of the totaldeposition amount of the two layers in the same way as that describedabove. In particular, the release property tends to be improved more inthe case where the deposition amount of the second layer on theultrathin copper foil side is smaller than the deposition amount of thefirst layer on the carrier foil side.

Further, for preventing oxidation of the ultrathin copper foil surface,a release layer may be provided with an anti-oxidation layer made of alow melting point metal. The low melting point metal is a metal having amelting point of 450° C. or less alone or its alloy. Specifically,depositing Zn, Sn, Bi, In, or an alloy containing as a principalingredient one element among Zn, Sn, Pb, Bi, and In has an effect ofsuppressing discoloration of the ultrathin copper foil surface due tooxidation, so is preferred.

The ultrathin copper foil is formed on the release layer by electrolyticplating using a copper sulfate bath, copper pyrophosphate bath, coppersulfamate bath, copper cyanide bath, or the like. Note that, as theplating bath, preferably use is made of a copper plating bath having apH within a range of 1 to 12.

In the formation of the ultrathin copper foil, when the surface of therelease layer is formed by Zn or another metal which is easily dissolvedin the plating solution, the dip time and/or current value in theplating solution, the removal of the plating solution and/or rinsing inthe plating finishing step, the pH of the plating solution immediatelyafter the metal plating, etc. determine the residual state of therelease layer, therefore the bath type must be selected according to therelationship between the release layer surface and the metal formed onthat.

Further, in the formation of ultrathin copper foil on a release layer,it is very difficult to perform uniform plating due to the releaseproperty of the release layer, therefore, as a result, there aresometimes many pinholes in the ultrathin copper foil. At the time ofsuch a plating condition, by first performing strike copper plating,then performing the usual electrolytic plating, the release layer can beuniformly plated and the number of pinholes formed in the ultrathincopper foil can be sharply decreased.

The thickness of the copper plating deposited by the strike plating ispreferably 0.01 μm to 1 μm. There are a variety of conditions dependingon the bath types, but preferably the current density is 0.1 A/dm² to 20A/dm², and the plating time is 0.1 second or more. If the currentdensity is less than 0.1 A/dm², it is difficult to uniformly plate therelease layer, while when it exceeds 20 A/dm², in strike platingreducing the metal concentration of the plating solution, a burntplating occurs and a uniform copper plating layer is not obtained, sothis is not preferred. A plating time less than 0.1 second is too shortto obtain a sufficient plating layer, so is not preferred.

After forming a copper plating layer having a thickness of 0.01 μm ormore not degrading the release property of the release layer on therelease layer by strike plating, copper is plated to a desired thicknessto thereby obtain an ultrathin copper foil.

Further, when including P in the ultrathin copper foil surface at theside contacting the release layer, the adhesion with the release layeris weakened, therefore the peeling strength becomes smaller.Accordingly, in order to adjust the peeling strength, it is effective toinclude P in the ultrathin copper foil surface at the release layerside.

Note that in order to obtain greater strength adhesion with theinsulating substrate at the ultrathin copper foil surface (surface notcontacting release layer), the surface of the ultrathin copper foil maybe roughened to give a roughness of the surface Rz of 0.2 to 3.0 (μm).This is because, if the roughness is less than 0.2 (μm), the rougheningdoes not influence the adhesion so much, therefore is meaningless, whilewhen the roughness is 3 (μm), a sufficient adhesion is obtained,therefore roughening exceeding that is not required.

Finally, Ni and Zn having effects for rust prevention and heatresistance or, according to a certain case, Cr are deposited onto theroughened surface. Further, in order to improve the peel strength, thecoating of silane is effective.

EXAMPLES

Below, the present invention will be specifically explained according toexamples.

The plating conditions of the examples are as follows.

(1) Copper Plating Conditions

<Copper Plating Conditions 1>

Cu₂P₂O₇3H₂O: 3 to 50 g/liter

K₄P₂O₇: 50 to 350 g/liter

pH: 8 to 11

Current density: 0.1 to 5 A/dm²

<Copper Plating Conditions 2>

Cu₂P₂O₇3H₂O: 10 to 150 g/liter

K₄P₂O₇: 50 to 400 g/liter

NH₃OH (28%): 1 to 10 ml/l

pH: 8 to 12

Bath temperature: 20 to 60° C.

<Copper Plating Conditions 3>

Copper sulfate (as Cu metal): 10 to 70 g/dm³

Sulfuric acid: 30 to 120 g/dm³

Current density: 1 to 60 A/dm²

Power supply time: 1 second to 2 minutes

Bath temperature: 10 to 70° C.

(2) Nickel Plating Conditions

Nickel sulfate (as Ni): 1 to 120 g/dm³

Boric acid: 10 to 50 g/dm³

Current density: 1 to 60 A/dm²

Power supply time: 1 second to 2 minutes

Bath temperature: 10 to 70° C.

(3) Mo—Co Plating Conditions

Co amount: 0.1 to 20 g/dm³

Mo amount: 0.05 to 20 g/dm³

Citric acid: 5 to 240 g/dm³

Current density: 0.1 to 60 A/dm²

Power supply time: 1 second to 5 minutes

Bath temperature: 10° C. to 70° C.

(4) Mo—Ni Plating Conditions

Ni sulfate hexahydrate: 10 to 100 g/dm³

Sodium molybdate dihydrate: 10 to 100 g/dm³

Sodium citrate: 30 to 200 g/dm³

Bath temperature: 10 to 50° C.

Current density: 0.5 to 15 A/dm²

(5) W—Ni Plating Conditions

Ni sulfate hexahydrate: 10 to 100 g/dm³

Sodium tungstate dihydrate: 10 to 100 g/dm³

Sodium citrate: 30 to 200 g/dm³

Bath temperature: 30 to 90° C.

Current density: 0.5 to 15 A/dm²

Example 1

Production of Ultrathin Copper Foil with Carrier By Carrier Foil→Mo—Co(Release Layer)→Copper Plating (Ultrathin Copper Foil)

A copper foil having one surface with an Rz of 0.8 μm (thickness: 31 μm)was used as the carrier foil. A release layer was formed by Mo—Coplating under the following conditions:

Co amount: 4.0 g/dm³

Mo amount: 2.0 g/dm³

Citric acid: 80 g/dm³

Current density: 2 A/dm²

Power supply time: 15 seconds

Bath temperature: 50° C.

The deposition amount of the formed release layer was 1.5 mg/dm², andMo/(Mo+Co)*100 was equal to 31(%).

The formed release layer was plated with copper to a thickness of 0.2 μmunder the above Copper Plating Conditions 1, then was plated with copperover that according to the above Copper Plating Conditions 3 with acurrent density of 4.5 A/dm² to form an ultrathin copper foil having athickness of 3 μm and thereby obtain an ultrathin copper foil with acarrier.

Then, the surface was treated by Ni: 0.5 mg/dm², Zn: 0.05 mg/dm², andCr: 0.3 mg/dm², then was treated by a silane coupling agent(post-treatment) to obtain the ultrathin copper foil with the carrier.

Example 2

Production of Ultrathin Copper Foil with Carrier by Carrier Foil→Mo—Ni(Release Layer)→Copper Plating (Ultrathin Copper Foil)

A copper foil having one surface with an Rz of 0.85 μm (thickness: 31μm) was used as the carrier copper foil. This was plated under thefollowing conditions to prepare an Mo—Ni plating layer:

Ni sulfate hexahydrate: 50 g/dm³

Sodium molybdate dihydrate: 60 g/dm³

Sodium citrate: 90 g/dm³

Bath temperature: 30° C.

Current density: 3 A/dm²

Power supply time: 20 seconds

The deposition amount of the prepared release layer was 2.4 mg/dm², andMo/(Mo+Ni)*100 was equal to 29(%)

The release layer was formed with a copper plating layer having athickness of 0.2 μm according to the Copper Plating Conditions 1, thenwas further formed with a copper plating layer by plating having acurrent density of 4.5 A/dm² by using the Copper Plating Conditions 3 toform an ultrathin copper foil having a thickness of 3 μm and obtain anultrathin copper foil with a carrier.

Then, the surface was treated by Ni: 0.5 mg/dm², Zn: 0.05 mg/dm², andCr: 0.3 mg/dm² and was treated by a silane coupling agent(post-treatment) to obtain the ultrathin copper foil with the carrier.

Example 3

Production of Ultrathin Copper Foil with Carrier By Carrier Foil→W—Ni(Release Layer)→Copper Plating (Ultrathin Copper Foil)

A copper foil having one surface with an Rz of 0.82 μm (thickness: 31μm) was used as the carrier copper foil. This was plated under thefollowing conditions to prepare a W—Ni layer:

Ni sulfate hexahydrate: 50 g/dm³

Sodium tungstate dihydrate: 60 g/dm³

Sodium citrate: 90 g/dm³

Bath temperature: 70° C.

Current density: 2.5 A/dm²

Power supply time: 18 seconds

The deposition amount of the prepared release layer was 1 mg/dm², andW/(W+Ni)*100=20%

The release layer was plated with copper to a 0.2 μm thickness accordingto the above Copper Plating Conditions 1, then was further plated with acurrent density of 3.5 A/dm² under the Copper Plating Conditions 3 toform an ultrathin copper foil having a thickness of 3 μm and therebyobtain an ultrathin copper foil with a carrier.

Then, the surface was treated with Ni: 0.5 mg/dm², Zn: 0.05 mg/dm², andCr: 0.3 mg/dm², then was treated by a silane coupling agent(post-treatment) to obtain an ultrathin copper foil with a carrier.

Example 4

Production of Ultrathin Copper Foil with Carrier By Carrier Foil→Mo—Co(First Layer)→Mo—Co (Second Layer) (Release Layer)→Copper Plating(Ultrathin Copper Foil)

A copper foil having one surface with an Rz of 0.74 μm (thickness: 22μm) was used as the carrier copper foil. This was plated under thefollowing conditions to prepare Mo—Co plating layers:

<First Layer Plating Conditions>

Co amount: 4.0 g/dm³

Mo amount: 3.0 g/dm³

Citric acid: 80 g/dm³

Current density: 2 A/dm²

Power supply time: 10 seconds

Bath temperature: 50° C.

<Second Layer Plating Conditions>

Co amount: 4.0 g/dm³

Mo amount: 1.5 g/dm³

Citric acid: 80 g/dm³

Current density: 2 A/dm²

Power supply time: 5 seconds

Bath temperature: 50° C.

The total deposition amount of the release layers (first layer+secondlayer): 2.3 mg/dm², and

First layer of Mo/(Mo+Co)*100=56%, and

Second layer of Mo/(Mo+Co)*100=23% were formed.

The release layers were formed with copper plating to 0.2 μm thicknessby the Copper Plating Conditions 1, then were further plated using theCopper Plating Conditions 3 with a current density of 3.5 A/dm² to forman ultrathin copper foil having a thickness of 3 μm and thereby obtainthe ultrathin copper foil with the carrier.

Then, the surface was treated with Ni: 0.5 mg/dm², Zn: 0.05 mg/dm², andCr: 0.3 mg/dm², then as treated with a silane coupling agent(post-treatment) to obtain an ultrathin copper foil with a carrier.

Comparative Example 1

1. Carrier Foil

A copper foil having a surface roughness Rz of the carrier foil of 1.2μm was used as the carrier foil.

2. Formation of Release Layer

Cr metal was deposited onto the carrier copper foil to form a releaselayer.

3. Formation of Ultrathin Copper Foil

The release layer was plated with copper to a thickness of 1 μm underthe conditions of:

Cu₂P₂O₇.3H₂O: 30 g/liter

K₄P₂O₇: 300 g/liter

pH: 8

Current density: 4 A/dm²,

then was electroplated under the conditions of:

Cu concentration: 50 g/liter

H₂SO₄: 100 g/liter

Current density: 20 A/dm²

to obtain an ultrathin copper foil having a thickness of 3 μm. This wasfurther roughened by depositing particles of copper according to a knownmethod.

The roughened ultrathin copper layer was plated by zinc and treated bychromate according to known methods as the rust prevention treatment andsurface treatment to obtain an ultrathin copper foil with a carrier.

Comparative Example 2

1. Carrier Foil

A copper foil having a surface roughness Rz of the carrier foil of 1.2μm was used as the carrier foil.

2. Formation of Release Layer

The carrier copper foil was electroplated by Cr continuously to form aCr plated release layer having a deposition amount of 1.5 mg/dm². Ahydrated oxide was formed on the surface layer.

3. Formation of Ultrathin Copper Foil

This Cr plated release layer was plated with copper by strike platingfor 60 seconds under the conditions of:

Cu₂P₂O₇.3H₂O: 30 g/liter

K₄P₂O₇: 300 g/liter

pH: 8

Current density: 1.5 A/dm²,

then was plated with copper to a thickness of 1 μm under the conditionsof:

Cu₂P₂O₇.3H₂O: 30 g/liter

K₄P₂O₇: 300 g/liter

pH: 8

Current density: 4 A/dm²,

then was electroplated under the conditions of:

Cu concentration: 50 g/liter

H₂SO₄: 100 g/liter

Current density: 20 A/dm²

to obtain an ultrathin copper foil having a thickness of 3 μm andfurther was roughened by depositing particles of copper according to aknown method.

The roughened ultrathin copper layer was plated by zinc and treated bychromate according to known methods as the rust prevention treatment andsurface treatment to obtain an ultrathin copper foil with a carrier.

<Evaluation>

Samples for evaluation of the carrier peeling force of the ultrathincopper foils with carriers prepared in the above examples andcomparative examples were prepared and evaluated as follows.

(1) Samples for Measurement of Carrier Peeling Force and Confirmation ofBlistering

The ultrathin copper foils with carriers (Examples 1 to 4 andComparative Examples 1 and 2) were cut into pieces each having a size of250 mm in the vertical direction and 250 mm in the horizontal direction.These were then heated at a temperature of 350° C. for 10 minutes toprepare samples for confirmation of blistering.

Further, resin substrates were adhered to the ultrathin copper foilsides of above heat treated samples by double-sided tape to therebyobtain single-sided copper-clad multilayer for measurement of thepolyimide carrier peeling force.

(2) Samples for Confirmation of Pinholes

The ultrathin copper foils with carriers (Examples 1 to 4 andComparative Examples 1 and 2) were cut into pieces each having a size of250 mm in vertical direction and 250 mm in horizontal direction.Transparent tapes were adhered to the ultrathin copper foil sides. Theultrathin copper foils were peeled from the carrier foils to therebyobtain samples for confirmation of pinholes.

<Evaluation of Characteristics of Ultrathin Copper Foils>

(1) Method of Measurement of Carrier Peeling Force and Confirmation ofBlistering

(a) Confirmation of Blistering

Whether or not the ultrathin copper foils on the carrier foils swelledup was visually examined. The number of blisters was counted. Theresults are shown in Table 1.

(b) Measurement of Carrier Peeling Force

The samples prepared according to the method of (1) described above weremeasured for carrier peeling force (peeling strength) for n=3 number ofspecimens by peeling off the ultrathin copper foils from the carrierfoils with a measured specimen width of 10 mm according to the methodprescribed in JIS C6511. The results of the evaluation are shown inTable 1.

(c) Confirmation of Pinholes

Light was irradiated against the pinhole measurement samples of theabove (2) from their bottoms. The numbers of spots of light were countedand used as the numbers of pinholes.

TABLE 1 Release layer Carrier Number forming peeling of metalComposition force Number of blisters A B (%) (KN/m) pinholes measuredExample 1 Mo Co 31 0.075 1 1 Example 2 Mo Ni 29 0.085 1 0 Example 3 W Ni20 0.06 0 0 Example 4 Mo Co First 0.035 0 0 layer: 56 Second layer: 23Comp. Ex. 1 Cr — 0.35 15 1 Comp. Ex. 2 Cr — 0.03 2 14

<Results of Evaluation>

The ultrathin copper foil with the carrier of Comparative Example 1 hada high carrier peeling force and a few blisters. On the other hand, theultrathin copper foil with the carrier of Comparative Example 2 had alow carrier peeling force and many blisters. In this way, thecomparative examples exhibited the tendencies that the lower the carrierpeeling force, the larger the number of blisters and the smaller thenumber of blisters, the higher the carrier peeling force.

Contrary to this, the ultrathin copper foils with carriers of thepresent invention had low carrier peel forces and few blisters.

The ultrathin copper foils with carriers of the present invention arestabler in both of the blistering and carrier peeling force incomparison with the conventional ultrathin copper foils with carriers inwhich the principal ingredient of the release layer is Cr such as shownin the comparative examples.

Further, by providing two layers with different composition ratios ofmetals of the two ingredients forming the release layers and changingthe composition ratio between the portion contacting the carrier foilside and the portion contacting the ultrathin copper foil, a more stableultrathin copper foil with a carrier is obtained.

Further, in the present age where environmental problems have becomeserious, little or no Cr is used, therefore the ultrathin copper foilwith the carrier of the present invention is environmentally friendly.

In the above examples, as release layers, use was made of layers ofMo—Co, Mo—Ni, and W—Ni, but other than these, the same effects areobtained even by combinations of Mo—Fe, V—Fe, V—Co, V—Ni, Mn—Fe, Mn—Co,Mn—Ni, W—Fe, and W—Co.

As explained above, the present invention can provide an ultrathincopper foil with a carrier suppressing the occurrence of blistering atthe release layer interface without exerting an influence upon thecarrier peeling force, friendly to the environment, and enabling easypeeling apart of the carrier foil and the ultrathin copper foil evenwhen under a high temperature environment.

Further, the present invention has the excellent effect that a printedcircuit board stable in production quality can be provided as the baseof a printed circuit board for fine pattern applications using theultrathin copper foil with the carrier, a multi-layer printed circuitboard, a chip-on-film use circuit board, or the like.

While the invention has been described with reference to specificembodiments chosen for purpose of illustration, it should be apparentthat numerous modifications could be made thereto by those skilled inthe art without departing from the basic concept and scope of theinvention.

1. An ultrathin copper foil with a carrier comprising a carrier foil, afirst release layer and a second release layer, and an ultrathin copperfoil, said first release layer consisting of a metal A for retaining arelease property and a metal B which is a different metal from saidmetal A for facilitating plating of the ultrathin copper foil, saidsecond release layer consisting of the metal A and the metal B, and saidfirst release layer and second release layer are both chromium-free. 2.The ultrathin copper foil with a carrier of claim 1, wherein said firstrelease and second release layer have composition ratios of the metal Aand the metal B respectively, said composition ratios are defined by thefollowing equation:|c/(c+d)−e/(e+f)|*100≧3 where, c is the content in weight of the metal Ain said first release layer, d is the content in weight of the metal Bin said first release layer, e is the content in weight of the metal Ain said second release layer, and f is the content in weight of themetal B in said second release layer.
 3. An ultrathin copper foil withthe carrier of claim 2, wherein the metal A is Mo, Ta, V, Mn, or W, andthe metal B is Fe, Co, or Ni.
 4. An ultrathin copper foil with thecarrier of claim 3, wherein a total of the amount of deposition of saidfirst release layer and said second release layer is 0.05 mg/dm² to 50mg/dm².
 5. A printed circuit board for high density ultrafineinterconnect application comprising an ultrathin copper foil having thecarrier of claim 4 which is laminated on a resin substrate.
 6. A printedcircuit board for a high density ultrafine interconnect applicationcomprising an ultrathin copper foil having the carrier of claim 3 withthe ultrathin copper foil is laminated on a resin substrate.